1. Field of the Invention
The present invention relates to opto-electronic packages in which optical fibers are sealed, and more particularly to packages in which an optical integrated circuit controls optical fibers coupled thereto in conjunction with electrical leads coupled to the package.
2. History of the Prior Art
Opto-electronic devices are known in which the optical fibers are coupled for control in conjunction with electrical leads coupled to an optical integrated circuit (IOC). Examples of such devices include optical switches, lasers, detectors, amplifiers, and modulators. The optical integrated circuit switches the optical fiber inputs and outputs in response to signals provided on the electrical leads.
Opto-electronic devices of the type described are typically made by attaching an optical integrated circuit to a package body, wire bonding the optical integrated circuit to the body for coupling to leads attached to the body, optically aligning and attaching optical fibers to the optical integrated circuit, sealing the optical fibers to the package body, sealing a lid over the package body to provide an enclosed package, and anchoring the optical fibers at the opposite ends of the package. Many applications of the opto-electronic devices require hermetic sealing of the package body. Hermeticity requires that the enclosure be sealed, including the fiber interfaces therewith, with no organic material within the boundaries of the enclosure.
One conventional construction of an opto-electronic package for integrated sealing of optical fibers utilizes a separate submount assembly in conjunction with the package body. The submount, which defines a separate substrate for the package, has an optical integrated circuit mounted thereon together with fiber arrays at opposite sides of the optical integrated circuit. The optical integrated circuit is wire bonded to electrical connections on the submount, and the opposite fiber arrays are aligned and attached to the submount. The submount assembly is then placed within a package body in such a way that the opposite fiber arrays are threaded through end pipes at opposite ends of the package body. When the fiber arrays are positioned within the end pipes, the submount assembly is positioned in a central location within the package body, where it is secured to the body. The submount assembly is then wire bonded to electrical leads which extend into the interior of the package body from opposite sides thereof. The optical fiber arrays are then sealed within the end pipes. A lid for the package is placed over the open package body, and is sealed thereon such as by seam welding. The fiber arrays are then sealed at the fiber pipes, such as with cured epoxy, to complete the opto-electronic package.
Opto-electronic packages of the type described in the preceding paragraph suffer from a number of disadvantages. For one thing, the package must be large enough to thread the fiber arrays through the opposite end pipes without overstressing the fibers. Moreover, even with relatively large packages, the fibers must be bent when attaching the submount assembly. Even when the amount of fiber bending is minimized, fiber damage can occur with the result that signal insertion loss is increased and long term reliability problems sometimes arise. The opposite fiber arrays are jacketed at the outside of bare portions of the fibers. Because the jacketed portions of the fibers are substantially larger than the bare portions, apertures in the end pipes must be large enough for the jacketed portions to be threaded therethrough, even though the smaller bare portions of the fibers are sealed within the end pipes. The bare portions of the fibers are metallized, and sealing is accomplished by dispensing molten solder through vertical apertures in the end pipes. Because the apertures in the end pipes must be large enough to accommodate the jacketed portions of the fibers, they are relatively large, thereby requiring a large amount of solder to fill the apertures and accomplish sealing of the fibers thereto. Automated assembly of the opto-electronic package further requires the use of the separate submount assembly.
In an effort to eliminate some of the disadvantages of such conventional opto-electronic packages, alternative arrangements are sometimes used. In one such alternative arrangement, input/output fiber arrays are inserted into the package first, followed by optical alignment and attachment in the package. However, fiber array insertion is difficult to automate in such arrangement. While this approach does not require an increase in package size, the optical alignment process cannot be easily automated because the higher package walls get in the way of machine tooling. In a further alternative approach, the fibers are sealed in the fiber pipe before attaching this assembly to the package. However, the fiber pipe-to-package joint must be performed at a sufficiently low temperature to prevent the re-flow of the completed fiber seal. This leads to potential reliability problems, when the product is close to the end of the assembly cycle.
Briefly stated, the present invention provides an opto-electronic package for integrated sealing of optical fibers having an enclosed package which is split at or close to the plane of the fiber axes. This enables the fibers to be laid in the package body with the opposing lid then being placed over the body to form the enclosed package. Threading of the fibers through the opposite end pipes is eliminated, with the result that the package can be made much smaller. Also, because the optical fibers are laid in rather than threaded, the opposite end pipes formed by mating portions of the package body and a lid need only have apertures therein which are very slightly larger than the fibers themselves, eliminating the large apertures which must be solder sealed in prior arrangements. It is not necessary to thread the jacketed portions of the optical fibers through the end pipes.
In opto-electronic packages according to the invention, automated techniques for fiber alignment and attachment can be accomplished without the need for an intermediate subassembly. The optical integrated circuit is mounted directly on the package base assembly and is wire bonded thereto to complete the required electrical interconnections. The package base may be built as a multi-layer ceramic substrate to provide the required electrical connectivity. Alternatively, the package may have a metal base. In either case, a metal seal ring is used for fiber sealing. The package lid is designed to have the necessary mating features such as to provide the fiber feedthrough for optical fiber sealing and fiber jacket strain relief. The optical fibers can be fully terminated at both ends prior to the final assembly and package sealing operations. The package lid may be sealed to the package body such as by using solder sealing. The optical fibers can be sealed to the assembled package such as by solder sealing metal coated fibers, solder sealing bare fibers, or low temperature glass sealing. The package lid can be sealed in place prior to the sealing of the optical fibers at the opposite ends of the package. However, because both sealing operations typically involve solder sealing, they can be accomplished simultaneously, thereby improving over prior art arrangements in which separate lid and fiber sealing are required.